66 



BIOLOGY OF THE PROTOZOA 



first post-fertilization division of the cell, and each daughter-nucleus 

 divides three times. 



(/;) Linin.^The achromatic reticulum of the nucleus appears to 

 be continuous with the alveolar reticulum of the cytoplasm, the 



Fig. 28. — Origin of macronucleus after conjugation in Urolcptus mohilis. (1) 

 First metagamic mitosis of the amphinucleus; (2) one of the progeny of this division 

 dividing again; (3), (4), (5) telophase stages of second division of the amphinucleus 

 resulting in a new macronucleus (above), and a degenerating nucleus (below); (6 to 

 10), stages in differentiation of the yovuig macronucleus and disintegration and 

 absorption of the old macronucleus; in (10) two new micronuclei are in mitosis 

 preparatory to the first division of the ex-conjugant. (M) new macronucleus; (m) new 

 micronuclei; {d) degenerating old macronuclei. (.\fter Calkins.) 



continuity of protoplasmic stuffs being unbroken in the living 

 organism. In fixed and stained cells, however, unless the fixation 

 is perfect, there is very apt to be a clear space between the nuclear 

 membrane and the c\'toplasin. Such j^erinuclear spaces are due 

 to the shrinkage accompanying coagulation of the colloidal proto- 



